Non-catalyzed cathodic oxygen reduction at graphite granules in microbial fuel cells

Oxygen is the most sustainable electron acceptor currently available for microbial fuel cell (MFC) cathodes. However, its high overpotential for reduction to water limits the current that can be produced. Several materials and catalysts have previously been investigated in order to facilitate oxygen reduction at the cathode surface. This study shows that significant stable currents can be delivered by using a non-catalyzed cathode made of granular graphite. Power outputs up to 21 W m⁻³ (cathode total volume) or 50 W m⁻³ (cathode liquid volume) were attained in a continuous MFC fed with acetate. These values are higher than those obtained in several other studies using catalyzed graphite in various forms. The presence of nanoscale pores on granular graphite provides a high surface area for oxygen reduction. The current generated with this cathode can sustain an anodic volume specific COD removal rate of 1.46 kg_COD m⁻³ d⁻¹, which is higher than that of a conventional aerobic process. This study demonstrates that microbial fuel cells can be operated efficiently using high surface graphite as cathode material. This implies that research on microbial fuel cell cathodes should not only focus on catalysts, but also on high surface area materials.     

Effect of temperature on the performance of microbial fuel cells

Single and double chamber microbial fuel cells (MFCs) were tested in batch mode at different temperatures ranging from 4 to 35 °C; results were analysed in terms of efficiency in soluble organic matter removal and capability of energy generation. Brewery wastewater diluted in domestic wastewater (initial soluble chemical oxygen demand of 1200 and 492 mg L⁻¹ of volatile suspended solids) was the source of carbon and inoculum for the experiments. Control reactors (sealed container with support for biofilm formation) as well as baseline reactors (sealed container with no support) were run in parallel to the MFCs at each temperature to assess the differences between water treatment including electrochemical processes and conventional anaerobic digestion (in the presence of a biofilm, or by planktonic cells). MFCs showed improvements regarding rate and extent of COD removal in comparison to control and baseline reactors at low temperatures (4, 8 and 15 °C), whilst differences became negligible at higher temperatures (20, 25, 30 and 35 °C). Temperature was a crucial factor in the yield of MFCs both, for COD removal and electricity production, with results that ranged from 58% final COD removal and maximum power of 15.1 mW m⁻³ reactor (8.1 mW m⁻² cathode) during polarization at 4 °C, to 94% final COD removal and maximum power of 174.0 mW m⁻³ reactor (92.8 mW m⁻² cathode) at 35 °C for single chamber MFCs with carbon cloth-based cathodes. Bioelectrochemical processes in these MFCs were found to have a temperature coefficient, Q10 of 1.6.A membrane-based cathode configuration was tested and gave promising results at 4 °C, where a maximum power output of 294.6 mW m⁻³ reactor (98.1 mW m⁻² cathode) was obtained during polarization and a maximum Coulombic efficiency (Y_Q) of 25% was achieved. This exceeded the performance at 35 °C with cloth-based cathodes (174.0 mW m⁻³; Y_Q 1.76%).     

The internal resistance of a microbial fuel cell and its dependence on cell design and operating conditions

The internal resistance R_int of a mediator-less microbial fuel cell (MFC) has been determined as a function of cell voltage using electrochemical impedance spectroscopy (EIS) for a MFC with and without Shewanella oneidensis MR-1. The same tests were performed for a MFC containing small stainless steel (SS) balls in the anode compartment with a graphite feeder electrode as in a packed bed cell. It has been found that R_int decreased with decreasing cell voltage as the increasing current flow decreases the polarization resistance of the anode and the cathode. The ohmic components of R_int played a very minor role. In the presence of MR-1 R_int was lower by a factor of about 100 than R_int of the MFC with buffer and lactate as anolyte. R_int was also significantly lower for the anode containing SS balls with buffer and lactate as anolyte. For the MFC containing SS balls in the anode compartment no significant further decrease of R_int could be obtained when MR-1 was added to the anolyte since in this case the polarization resistance of the anode was lower than that of the cathode. Similar trends were observed in the cell voltage (V)-current (I) curves that were obtained using potentiodynamic sweeps and the power (P)-V curves that were calculated from the V-I curves.     

On the repeatability and reproducibility of experimental two-chambered microbial fuel cells

The capability of the experimental systems used in two-chambered microbial fuel cell experimentation was tested in terms of repeatability and reproducibility. The optimal number of replicates needed to discriminate between responses of technical interest, both in open-circuit and closed-circuit experiments was studied. For N = 4 replicates, these differences were set to 9.0% COD_R units, 261 mV and 63 mg/L in VFAs for open-circuit experiments and 3.6%, 30.2 mV and 45 mg/L in closed circuit experiments. Cycling operation with several reactor refills using fresh wastewater and keeping the same biofilm between cycles almost has no influence in COD_R and VFAs but voltage standard deviation reduces by one half between the first and fourth cycle. This study takes part by the option of increasing the number of replicates because although it may have lower repeatability, the amount of data generated per unit time is larger than running the experiments in cycles.     

Multi-objective steady-state optimization of two-chamber microbial fuel cells

A microbial fuel cell (MFC) is a novel promising technology for simultaneous renewable electricity generation and wastewater treatment. Three non-comparable objectives, i.e. power density, attainable current density and waste removal ratio, are often conflicting. A thorough understanding of the relationship among these three con-flicting objectives can be greatly helpful to assist in optimal operation of MFC system. In this study, a multi-objective genetic algorithm is used to simultaneously maximizing power density, attainable current density and waste removal ratio based on a mathematical model for an acetate two-chamber MFC. Moreover, the level diagrams method is utilized to aid in graphical visualization of Pareto front and decision making. Three bi-objective optimization problems and one three-objective optimization problem are thoroughly investigated. The obtained Pareto fronts illustrate the complex relationships among these three objectives, which is helpful for final decision support. Therefore, the integrated methodology of a multi-objective genetic algorithm and a graphical visualization technique provides a promising tool for the optimal operation of MFCs by simultaneously considering multiple conflicting objectives.     

Performance of anaerobic fluidized bed microbial fuel cell with different porous anodes

Anode materials were used to construct microbial fuel cells(MFCs), and the characteristics of the anodes were important for successful applied performance of the MFCs. Via the cyclic voltammetry(CV) method, the experiments showed that 5 wt% multiwalled carbon nanotubes(MWNTs) were optimal for the PANI/MWNT film anodes prepared using 24 polymerization cycles. The maximum output voltage of the PANI/MWNT film anodes reached 967.7 mV with a power density of 286.63 mW·m~(-2). Stable output voltages of 860 mV, 850 mV, and870 mV were achieved when the anaerobic fluidized bed microbial fuel cell(AFBMFC) anodes consisted of carbon cloth with carbon black on one side, copper foam and carbon brushes, respectively. Pretreatment of the anodes before starting the AFBMFC by immersion in a stirred bacterial fluid significantly shortened the AFBMFC startup time. After the AFBMFC was continuously run, the anode surfaces generated active microbial catalytic material.     

微生物燃料电池阳极产电微生物研究进展

微生物燃料电池（Microbial fuel cells,简称 MFCs）是一种生物电化学混合系统,利用微生物的氧化代谢作用将有机物或者无机物中的能量转化为电能,具有节能、减少污泥生成及能量转换的突出优势,目前得到研究者们的广泛关注。其中产电微生物是MFCs系统的核心组成部分,筛选及培养高效产电微生物对促进MFCs的产电性能具有重要作用。通过对产电微生物电子传递机制、产电微生物种类以及影响微生物产电的因素进行分析总结,综述了阳极产电微生物的最新研究进展,最后从微生物角度展望了未来的研究方向,以期为产电微生物在MFCs中的应用提供指导和支持。     

微生物燃料电池的研究进展

介绍了微生物燃料电池的工作原理。列举了微生物燃料电池的3个实例模型。概括了微生物燃料电池目前存在的问题和解决方法。展望了微生物燃料电池的应用前景。     

Investigation of ionic polymer cathode binders for microbial fuel cells

Microbial fuel cell (MFC) air cathodes examined here were made using poly(phenylsulfone) (Radel^®) binders sulfonated to various ion exchange capacities (IECs). We examined the effect of increasing the IEC of poly(phenylsulfone) Radel binders from 0 to 2.54 meq/g on cathode performance using linear sweep voltammetry (LSV), impedance, and single chamber air-cathode MFC tests. Unsulfonated Radel, which is a non-ionic, hydrophobic polymer, showed the highest current in LSV tests and the lowest charge transfer resistance. Increasing the binder IEC resulted in a decreased current response in LSV tests and an increased charge transfer resistance from 8 to 23 Ω. It is proposed that the presence of sulfonate groups in the cathode binder impeded the oxygen reduction activity of the cathodes by adsorption of the sulfonate to catalytic sites and by impeding proton diffusion to the catalyst surface. The unsulfonated Radel binder produced the most stable performance, and eventually the highest power density, in MFCs operated over 20 cycles (55 days). These results suggest that the use of a non-ionic binder is advantageous in an MFC cathode to facilitate charge transfer and stable performance in the neutral pH conditions found in MFCs.     

微生物燃料电池研究和应用方面的最新进展

微生物燃料电池是一种利用微生物的催化作用将化学能转变为电能的生物装置。微生物燃料电池在作为可替代性能源、新颖的污水处理方法以及氧和污染物的生物传感器等方面具有较大的潜能,但仍需进一步优化。本文确定了限制微生物燃料电池应用操作的几种因素,并在其性能提高方面进行了探讨。     

On the electrochemical performance of anthracite-based graphite materials as anodes in lithium-ion batteries

The electrochemical performance as potential negative electrode in lithium-ion batteries of graphite materials that were prepared from two Spanish anthracites of different characteristics by heat treatment in the temperature interval 2400-2800 °C are investigated by galvanostatic cycling. The interlayer spacing, d₀₀₂, and crystallite sizes along the c axis, L_c, and the a axis, L_a, calculated from X-ray diffractometry (XRD) as well as the relative intensity of the Raman D-band, I_D/I_t, are used to assess the degree of structural order of the graphite materials. The galvanostatic cycling are carried out in the 2.1-0.003 V potential range at a constant current and C/10 rate during 50 cycles versus Li/Li⁺. Larger reversible lithium storage capacities are obtained from those anthracite-based graphite materials with higher structural order and crystal orientation. Reasonably good linear correlations were attained between the electrode reversible charge and the materials XRD and Raman crystal parameters. The graphite materials prepared show excellent cyclability as well as low irreversible charge; the reversible capacity being up to ∼250 mA h g⁻¹. From this study, the utilization of anthracite-based graphite materials as negative electrode in lithium-ion batteries appears feasible. Nevertheless, additional work should be done to improve the structural order of the graphite materials prepared and therefore, the reversible capacity.     

A tubular microbial fuel cell

Cell potential and power performance for tubular microbial fuel cells utilising manure as fuel are reported. The microbial fuel cells do not use a mediator, catalysts or a proton exchange membrane. The cell design has been scaled up to a size of 1.8 m in length using electrodes of 0.4 m² in area. The cell does not require a strictly controlled anaerobic environment and has potential practical applications when adapted into the form of a helix allowing fuel to flow through it. The cell could be used for power generation in remote applications. The peak power density of the cell is over 3 μW cm ⁻² (30 mW m⁻²). The performance can be improved by a more effective design of the interface between the anode and cathode chambers.     

导电聚合物修饰微生物燃料电池阳极的研究进展

阳极作为微生物燃料电池的重要组成部分,其性能直接影响微生物燃料电池的产电效率。主要综述了聚苯胺、聚吡咯等导电聚合物及其复合物修饰微生物燃料电池阳极材料的最新研究进展,对修饰材料的特点与性能进行了分析,最后对导电聚合物修饰微生物燃料电池阳极进行了展望。     

Production of electricity from the treatment of continuous brewery wastewater using a microbial fuel cell

A single air-cathode microbial fuel cell (MFC) was constructed, carbon fiber was used as anode and continuous brewery wastewater as substrate. The MFC displayed a maximum power of 24.1 W m⁻³ (669 mW m⁻²) and an internal resistance of 23.3 Ω running on raw wastewater (chemical oxygen demand (COD) = 1501 mg L⁻¹). The effect of phosphate buffer solution (PBS) addition and substrate concentration of wastewater on the performance of MFC was demonstrated. Data showed that both PBS addition and increase of substrate concentration had a favorable effect on the electrochemical performance and substrate removal efficiency of the MFC. However, it can be concluded from the polarization curve that MFC operated under raw brewery wastewater had a relatively low internal resistance, which resulted in a favorable performance of the MFC compared with other MFCs using raw wastewater. Thus it is feasible and sustainable in nature because of the utilization of raw wastewater as substrate for in situ power generation apart from treatment.     

Treatment of carbon cloth anodes for improving power generation in a dual‐chamber microbial fuel cell

BACKGROUND: For a microbial fuel cell (MFC), the anode material plays a crucial role in power output. RESULTS: A dual‐chamber MFC was constructed using carbon cloth (CC) anodes treated by concentrated nitric acid (CC‐A) and heated in a muffle furnace (CC‐H), respectively. The experiment results showed that the stable maximum voltages were 0.42–0.46 V for CC, 0.52–0.58 V for CC‐A and 0.80 V for CC‐H under the condition of a 1000 Ω external resistance, which were much higher than those reported in the literature so far. Moreover, the maximum power density of the CC‐H anode (687 mW m^?2) was larger than for the CC‐A anode (480 mW m^?2) and the CC anode (333 mW m^?2). Electrochemical impedance spectroscopy (EIS) results revealed that the internal resistance was 251 Ω for CC anode, 202 Ω for CC‐A anode and 162 Ω for CC‐H anode. Scanning electron microscopy (SEM) results indicated that the increase of power generation was attributed to the increase of bacteria counts attached to anodes. The power output of the MFC increased along with the increase of the N1s/C1s ratio, which was proved by X‐ray photoelectron spectroscopy (XPS) analysis. CONCLUSIONS: Carbon cloth anodes treated by concentrated nitric acid and high temperature resulted in improved power generation by a microbiol fuel cell. © 2012 Society of Chemical Industry     

The polarization behavior of the anode in a microbial fuel cell

Microbial fuel cell (MFC) systems are unique electrochemical devices that employ the catalytic action of bacteria to drive the oxidation of organic compounds. These systems have been suggested as renewable energy sources for small remote devices; however, questions remain about how MFCs can be efficiently optimized for this purpose. Several electrochemical techniques have been employed in this study to elucidate the limiting factors in power production by MFCs. Impedance spectra were collected for the anode and cathode at their open-circuit potential (OCP) before and after all other electrochemical tests. Cell voltage-current curves were obtained using a potential sweep technique and used to determine the maximum power available from the system. Potentiodynamic polarization in two different potential regions was used to determine the exchange current for the reaction occurring at the anode at its OCP and to explore the polarization behavior of the anode and the cathode in a wide potential range. Cyclic voltammetry was used to evaluate the redox activity of the anode. These techniques used in combination showed that the microorganism Shewanella oneidensis MR-1 is solely responsible for the observed decrease of the OCP of the anode, the increased rate of oxidation of lactate, the larger cell voltage and the increased maximum power output of the MFC.     

Electrochemical and gas phase parameters of cathodes for intermediate temperature solid oxide fuel cells

A series of cyclic voltammetry, chronoamperometry and electrochemical impedance experiments have been carried out in order to investigate the effect of cathode composition and porosity on the electrochemical characteristics of strontium-doped lanthanum, praseodymium and gadolinium cobaltite cathodes. The impedance responses at different electrode potentials of the half cell and symmetric single cell setups are compared and analyzed by the equivalent circuit modeling method. The deconvolution of impedance spectra for single cell cathode and anode reactions contributions based on the results of simultaneous analysis of half cells and symmetric single cells has been made by differential impedance real part vs. ac frequency plot analysis method. Noticeable influence of cathode chemical composition, meso-porosity and macro-porosity on the electrochemical activity of the oxygen electroreduction has been demonstrated. Seeming activation energy values have been calculated and discussed.     

Novel approach to membraneless direct methanol fuel cells using advanced 3D anodes

A conventional membrane electrode assembly (MEA) for a direct methanol fuel cell (DMFC) consists of a polymer electrolyte membrane (PEM) compressed between an anode and cathode electrode. Limitations with this conventional design include: cost, fuel crossover, membrane degradation or contamination, ohmic losses and reduced active triple phase boundary (TPB) sites for catalyst located away from the electrode/membrane interface. In this work, ex situ and in situ characterization of a novel electrode assembly based on a membraneless architecture and advanced 3D anodes was investigated. The approach was shown to be fuel independent and scaleable to a conventional bi-polar fuel cell arrangement. The membraneless configuration exhibits comparable performance to a conventional ambient (25 °C, 1 atm) air-breathing DMFC. However, it has the additional advantages of a simplified design, the elimination of the membrane (a significant component expense) and enhanced fuel and catalyst utilization through the extension of the active catalyst zone.     

Evaluation of catalytic properties of tungsten carbide for the anode of microbial fuel cells

In this communication we discuss the properties of tungsten carbide, WC, as anodic electrocatalyst for microbial fuel cell application. The electrocatalytic activity of tungsten carbide is evaluated in the light of its preparation procedure, its structural properties as well as the pH and the composition of the anolyte solution and the catalyst load. The activity of the noble-metal-free electrocatalyst towards the oxidation of several common microbial fermentation products (hydrogen, formate, lactate, ethanol) is studied for microbial fuel cell conditions (e.g., pH 5, room temperature and ambient pressure). Current densities of up to 8.8 mA cm⁻² are achieved for hydrogen (hydrogen saturated electrolyte solution), and up to 2 mA cm⁻² for formate and lactate, respectively. No activity was observed for ethanol electrooxidation.

The electrocatalytic activity and chemical stability of tungsten carbide is excellent in acidic to pH neutral potassium chloride electrolyte solutions, whereas higher phosphate concentrations at neutral pH support an oxidative degradation.     

Investigation of fuel and media flexible laminar flow-based fuel cells

We investigate the performance of air-breathing laminar flow-based fuel cells (LFFCs) operated with five different fuels (formic acid, methanol, ethanol, hydrazine, and sodium borohydride) in either acidic or alkaline media. The membraneless LFFC architecture enables interchangeable operation with different fuel and media combinations that are only limited by the actual anode catalyst used. Furthermore, operating under alkaline conditions significantly improves methanol and ethanol oxidation kinetics and stabilizes sodium borohydride. LFFCs operated with hydrazine and sodium borohydride as fuels exhibit power densities of 80 and 101 mW/cm², respectively. To optimize anode performance, particularly for ethanol electro-oxidation, we introduced a hydrogen cathode to the membraneless LFFC design which renders the cell an ideal platform for anode investigation. Here, we highlight two simple diagnostic methods, in situ single electrode studies and electrochemical impedance spectroscopy (EIS), for characterizing and optimizing the performance of a direct ethanol LFFC anode.